Wumpus

Copperbox revision 931.

I've added a module for drawing dots (the original Wumpus had quite a few dots so I've got a bit of code already written).

There's one problem though - the Multi constructor in Wumpus.Core.PictureInternal is meant to be a optimisation for drawing many primitives in one affine frame. Unfortunately + and X dots are both made of two independent line segments - they are multi-pictures already when multi-picture was supposed to represent many simple pictures (e.g. dots). I'm going to have to work out some trick (maybe dots as higher order functions) to accommodate many dots in one multi-picture.